1). Field of the Invention
This invention relates to a speaker.
2). Discussion of Related Art
It is often required that a speaker be mounted in, for example, a housing of a computer monitor or a housing of a television set. These housings generally do not provide space for large speakers. Speakers having magnetic fields leaking therefrom are preferably avoided due to the possibility of interference with a cathode ray tube. Ideally, such a speaker has a high sound pressure level output capability (volume), a wide frequency range, and low distortion.
The invention provides a speaker comprising a casing, a pole piece, a substantially circular magnetic structure, a diaphragm, a suspension mechanism, and an electric coil.
The casing has an inner surface and an outer surface. The pole piece is located within the casing. The pole piece has an outer surface, and an inner surface defining a venting passage therethrough. A substantially annular gap is defined between the inner surface of the casing and the outer surface of the pole piece.
The magnetic structure is located within the annular gap. The magnetic structure is radially polarized so as to have a first polarity on an inner surface and a second polarity on an outer surface so as to create a line of magnetic flux following a loop sequentially from the outer surface of the magnetic structure to the casing, from the casing to the pole piece, and from the pole piece to the inner surface of the magnetic structure.
The casing, the pole piece, and the magnetic structure are mounted to one another to form a magnet assembly which defines an annular coil gap with the path of the line of magnetic flux being across the coil gap.
The suspension mechanism has a first portion attached to the magnet assembly and a second portion attached to the diaphragm so as to mount the diaphragm to the suspension mechanism. The suspension mechanism allows for travel of the diaphragm relative to the magnet assembly. The diaphragm and the suspension mechanism jointly define an enclosure.
The coil is located in the coil gap and has a portion connected to the diaphragm so that an electric current in the coil causes movement of the diaphragm. Movement of the diaphragm causes movement of air through the venting passage between the enclosure and externally of the magnet assembly.
The travel of the diaphragm is preferably at least 0.1 times a diameter of the diaphragm in order to provide sufficient sound output.
The diaphragm preferably has a dome shape for sufficient stiffness at high frequencies.
The venting passage is preferably at least 0.5 times as wide as a diameter of the coil to ensure sufficient venting of air.
The venting passage is preferably at least 0.5 times as wide as a width of the diaphragm to ensure sufficient venting of air.
The electric coil preferably has a diameter that is at least 0.5 times as wide as the diaphragm in order to maximize the amount of force that can be generated when current flows through the coil.
A ratio of a length of the coil to a length of the coil gap preferably falls outside of the range of from 0.67 to 1.5 so as to allow for the travel to be sufficiently large without causing distortion. The ratio is preferably less than 0.67 so that the travel is relatively large thereby ensuring that the coil remains within the coil gap and so preventing distortion, while still minimizing coil mass and inductance.